Macular degeneration is a condition where the light-sensing cells of the macula, a near-center portion of the retina of the human eye, malfunction and slowly cease to work. Macular degeneration is the leading cause of central vision loss in people over the age of fifty years. Clinical and histologic evidence indicates that macular degeneration is in part caused by or results in an inflammatory process that ultimately causes destruction of the retina. The inflammatory process can result in direct destruction of the retina or destruction via formation of neovascular membranes which leak fluid and blood into the retina, quickly leading to scarring.
Many treatments for macular degeneration are aimed at stopping the neovascular (or “wet”) form of macular degeneration rather than geographic atrophy, or the “dry” form of Age-related Macular Degeneration (AMD). All wet AMD begins as dry AMD. Indeed, the current trend in advanced ophthalmic imaging is that wet AMD is being identified prior to loss of visual acuity. Treatments for macular degeneration include the use of medication injected directly into the eye (Anti-VEGF therapy) and laser therapy in combination with a targeting drug (photodynamic therapy); other treatments include brachytherapy (i.e., the local application of a material which generates beta-radiation).
Accurate alignment of a subject's eye is important in a number of situations. For example, when taking certain types of eye measurements, it is critical to know that the eye is in a particular reference position. When measuring the cornea of a patient's eye before therapeutic treatment, it can be important to repeat those measurements after the treatment to determine how much, if any, the treatment has affected the measurements. In order to accomplish this, one must ensure that the eye alignment is in the same position each time the particular measurements are made. Otherwise, the difference in data from before and after the treatment might be due to a change in eye alignment rather than the treatment.
A number of treatment and surgery procedures, typically involving irradiating one or more selected targets in the eye, require a patient's eye to be stabilized or positioned prior to and/or during treatment. For example, refractive laser surgery involves ablating corneal tissue of the eye with an ultra-fast, ultra-short pulse duration laser beam, to correct refractive errors in a patient's eye. As such, the patient's eye must be stabilized, and either the laser system must be properly and precisely aligned with the patient's eye, or the patient's eye must be properly and precisely aligned with the laser system. The eye is predisposed to saccades, which are fast, involuntary movements of small magnitude. A patient may voluntarily shift their gaze during surgery, and furthermore, eye position stability is affected by the patient's heartbeat and other physiological factors.
In order to achieve the goal of maximizing results while minimizing risks to the patient during such eye treatment, it is important to eliminate, or at least significantly reduce, as many system errors as possible. This includes the improper alignment of the patient's eye relative to the treatment system. Alignment errors may result from either a misconfiguration of the system, or from the patient's interaction with the system. Insofar as patient/system interaction is concerned, any voluntary or involuntary movement of the patient's eye during treatment can significantly alter the alignment of the eye relative to the treatment system. It is necessary, therefore, to hold the eye of the patient stationary during these procedures.
In addition, there is a need to control the distribution of radiation absorption by ocular structures during treatment, such as to assure an adequate dosage to a lesion being treated, and to avoid damaging collateral structures by stray radiation.